1. Field of the Invention
The present invention relates to a novel electrical resistance heating element for extremely high temperatures.
The heating element is intended for use in connection with heat treatment and sintering in inert and reducing atmospheres, in oxidizing atmospheres, and in a vacuum environment, up to extremely high temperatures, such as 2300° C.
2. Description of the Related Art
Resistance heating elements of the present type are manufactured by Applicant (Sandvik A B, of Sandviken, Sweden), such as resistance elements based on NiCr, FeCrAI, SiC, and MoSi2. These materials are used in a plurality of atmospheres and at mutually different temperatures. A common feature of these materials is that their usefulness at high temperatures, i.e., temperatures above 1300° C., is limited in reducing environments and under vacuum conditions.
Heating elements comprised primarily of Mo, W, Ta (tantalum),. and graphite are used for temperatures up to above 2000° C. Each of these materials has drawbacks and limitations, a common feature being that said materials oxidize readily when subjected to temperatures above 400-500° C., thereby requiring particular attention to be paid to furnace design and furnace operation. The high specific weight of Ta, Mo, and W also necessitates limitations with respect to mechanical construction. Further, material costs for refractory metals are high in themselves.